The Indian Navy’s Boeing P-8I long-range maritime patrol aircraft -- reputedly the world’s most fearsome submarine hunters -- have proved themselves in joint patrols with the United States Navy in the Indian Ocean, tracking Chinese submarines.

Last July, a pleased Indian Navy signed a billion-dollar contract with Boeing for four more P-8Is to augment the eight aircraft it already flies. Delivery will begin in 2020.

But, with Chinese submarine activity growing in the Indian Ocean, the navy wants more P-8Is on station.

The navy has now signed a $100-million contract, requiring Boeing to maintain spare parts and personnel in India, ready to respond to any defects or failures in the P-8I fleet over the next three years.

The so-called “performance-based logistics” contract requires Boeing to continue the warranty services it has so far provided under an initial production contract, which will expire in October.

“This contract will substantially bolster Boeing’s performance-based support to the Indian Navy and should maintain or increase the operational capability of the eight-aircraft fleet,” said Boeing.

Since the P-8I is based on a commercial Boeing 737-800/900 airliner, material support will also be sourced from the Boeing Commercial Aviation Services’ Fleet Services division. This is yet another lucrative triumph for Boeing, which has won more than $10 billion worth of Indian defence contracts since 2009.

Pratyush Kumar, president of Boeing India and vice president of Boeing International said, “With this contract, the Indian Navy can be assured of achieving exceptional operational capability and readiness of the P-8I fleet.”

Despite the navy’s growing reliance on the P-8I fleet, which has replaced ageing Soviet-era maritime patrol aircraft like the Tupolev-142 and Ilyushin-38, the navy’s P-8Is remain handicapped by New Delhi’s reluctance to sign a cooperation pact called the “Communications and Information Security Memorandum of Agreement”.

India’s refusal prevents Washington from providing “CISMOA-controlled” equipment, which would allow Indian and US submarines and P-8 aircraft to operate together smoothly.

To keep track of hostile submarines in the Bay of Bengal, the Arabian Sea and the Indian Ocean, naval pilots fly their P-8Is on eight-to-10 hour surveillance missions over these waters.

To strike enemy warships and submarines, the P-8I carries seven tonnes of weaponry on board, including advanced Harpoon missiles and heavyweight torpedoes.